diff --git a/layers/+filetree/neotree/packages.el b/layers/+filetree/neotree/packages.el
index ed88d5540..210194f86 100644
--- a/layers/+filetree/neotree/packages.el
+++ b/layers/+filetree/neotree/packages.el
@@ -111,4 +111,4 @@ Navigation^^^^             Actions^^         Visual actions/config^^^
 (defun neotree/pre-init-winum ()
   (spacemacs|use-package-add-hook winum
     :post-config
-    (setq winum-assign-func 'spacemacs//winum-neotree-assign-func)))
+    (add-to-list 'winum-assign-functions #'spacemacs//winum-neotree-assign-func)))
diff --git a/layers/+filetree/treemacs/packages.el b/layers/+filetree/treemacs/packages.el
index 8f321118b..8b233c8a0 100644
--- a/layers/+filetree/treemacs/packages.el
+++ b/layers/+filetree/treemacs/packages.el
@@ -71,4 +71,4 @@
 (defun treemacs/pre-init-winum ()
   (spacemacs|use-package-add-hook winum
     :post-config
-    (setq winum-assign-func #'treemacs--window-number-ten)))
+    (add-to-list 'winum-assign-functions #'treemacs--window-number-ten)))